1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to an electron gun in a color CRT(Cathode Ray Tube) for enhancing a resolution.
2. Background of the Related Art
In general, as shown in FIG. 1, the color CRT is provided with a panel 1, a funnel 2 of a bulb form welded to an inside surface of the panel, and a neck portion 5 at a rear of the funnel for sealing in the electron gun 4 to emit R. G. B beams 3 of red, green and blue colors. There is a coat 6 of fluorescent material of red, green, and blue colors on an inside surface of the panel, a support frame 8 in the vicinity of the coat of fluorescent material, and a shadow mask 7 fitted to the support frame 8 for selecting a color from the R. G. B beams 3 emitted from the electron gun 4. There is a deflection yoke 9 on an outer circumference of the funnel for deflecting the R. G. B beams emitted from the electron gun in a vertical or horizontal directions.
Referring to FIG. 2, the electron gun has a triode part and a main lens part. The triode part is provided with built-in heaters 4a, heat sources, three in-line cathodes 4b, a control electrode 4c for controlling thermal electrons emitted from the cathodes, and an accelerating electrode 4d for accelerating the thermal electrons, arranged in an order with certain gaps starting from the cathodes. The main lens part is provided with a focusing electrode 4e for focusing, and finally accelerating the R. G. B beams generated at the triode part, and an anode 4f. In the foregoing electron gun, there is a voltage difference occurred between the focusing electrode 4e and the anode 4f upon application of required voltages to respective electrodes, and the voltage difference forms an electrostatic lens between the electrodes. Accordingly, the R. G. B beams 3 from the triode part is focused in a course passing through the focusing electrode 4e and the anode 4f onto a center of the flourescent material coat by the electrostatic lens. In this instance, a self convergence deflection yoke 9 is come into operation for deflecting the R. G. B beams focused onto the center of the fluorescent material coat to an entire region of the screen.
A distribution of a magnetic field formed at the deflection yoke is as shown in FIGS. 3A and 3B. That is, a horizontal deflection magnetic field is formed in a pin cushion form, and a vertical deflection magnetic field is formed in a barrel form, for correction of mis-convergence in a peripheral region of the fluorescent material coat. As shown in FIGS. 3C and 3D, the horizontal deflection magnetic field and the vertical deflection magnetic field may be explained, with the horizontal deflection magnetic field and the vertical deflection magnetic field separated into two polar components and four polar components, respectively. That is, the two polar component deflects an electron beam in horizontal and vertical directions, and the four polar components converges the electron beam in a vertical direction and diverges in a horizontal direction. Therefore, even if a magnetic field is close to be uniform, the R. G. B beams receive substantial astigmatism in the peripheral region of the fluorescent material coat, such that a beam spot is distorted by fine pin cushion and barrel magnetic field components.
FIGS. 4A and 4B illustrate the electron beam spot distortion on a screen in more detail. That is, as there is no deflective magnetic field applied to the central portion of the screen, the electron beam spot shows no distortion. However, the R. G. B electron beams in the peripheral region are diverged in a horizontal direction and converged excessively in a vertical direction, the electron beams are elongated in horizontal direction substantially, and dispersed in up and down directions, to form a thin haze 11, that results in deterioration of the resolution in the peripheral region of the screen. This problem becomes the more serious as the CRT becomes the larger, and the deflection angle is the greater.
In order to solve the problem, in most cases of the related art, the astigmatism is corrected synchronous to a deflection signal when the electron beams are deflected toward the peripheral region of the screen, by providing a quadrupole between a first focusing electrode 41 and a second focusing electrode 42, which is provided by dividing the focusing electrode into two as shown in FIGS. 5A and 5B, that forms a quadrupole lens(see 13 in FIG. 6B). The system shown in FIGS. 5A and 5B is disclosed in U.S. Pat. No. 4,772,827, wherein the first focusing electrode 41 on the cathode side has electron beam pass through holes 41a, and vertical plate electrodes on both sides and between the electron beam pass through holes 41a. And, the second focusing electrode 42 having a high voltage applied thereto has horizontal plate electrodes 42b on upper and lower sides, and three electron beam pass through holes 42a corresponding to the electron beam pass through holes 41a in the first focusing electrode.
The operation of the foregoing electron gun will be explained with reference to FIGS. 5Axcx9c6B. The electron beams from the triode part(a beam forming region) pass through a first focusing electrode 41, a quadrupole part 41b on the first focusing electrode side, a quadrupole part 42b on the second focusing electrode side, and the second focusing electrode, and are focused at the eletrostatic lens 14 to form an image on the tube screen. Particularly, when the electron beam is deflected toward the peripheral region, though the first focusing electrode 41 is provided with a fixed static voltage, the second focusing electrode 42 is provided with a dynamic voltage varied with a required deflection of the electron beams. That is, as the voltages provided to the first focusing electrode 41 and the second focusing electrode 42 are provided to the quadrupole part 41b on the first focusing electrode side and the quadrupole part 42b on the second focusing electrode side, the quadrupole lens 13 is formed by the quadrupole, which corrects the astigmatism that affects the electron beams. In general, as a CRT becomes the larger, or the deflection angle becomes the greater, the dynamic voltage to the second focusing electrode is the higher than the static voltage to the first focusing electrode. A voltage difference between the first focusing electrode 41 and the second focusing electrode 42 form the quadrupole lens 13 at the quadrupole, which elongates the electron beams in a vertical direction. Accordingly, the quadrupole lens prevents the haze of the electron beams occurred when the electron beams are deflected to the peripheral region by a non-uniform magnetic field from the main lens 14 and the deflection yoke 9 in advance.
The quadrupole lens will be explained.
Referring to FIG. 6A, the electron beams 3 are focused at a central portion of the screen focused onto the central portion of the screen, the electron beams are not focused exactly due to a deflection aberration component when the electron beams are deflected to the peripheral region of the screen. And, portions shown in dashed lines on the drawing are an astigmatism component caused by the deflection yoke 9 when the electron beams are deflected to the peripheral region. A DY lens 12 formed by the deflection yoke 9 diverges the electron beams 3 in a horizontal direction and converges in a vertical direction. According to this, when the electron beams 3 are deflected to the peripheral region, an over-focusing component caused by a distance difference and an under-focusing component caused by the deflection yoke 9 are overlapped in the horizontal direction, to show a serious over-focusing, which results in a great dispersion of an image in the vertical direction, that deteriorates the resolution in the peripheral region. FIG. 6B illustrates the quadrupole lens added thereto for improving the above image dispersion, wherein it is shown that the astigmatism caused by the deflection yoke 9 is corrected by the quadrupole lens formed by the quadrupole. To do this, the quadrupole lens 13 is designed such that the electron beams are converged in the horizontal direction as much as a horizontal divergence caused by the deflection yoke and are diverged in the vertical direction as much as the vertical convergence caused by the deflection yoke. And, as shown in FIG. 6B, a lower dynamic voltage to a main lens forming electrode weakens the main lens, to permit the electron beams focused onto a point of the peripheral region in the horizontal/vertical directions. Thus, an appropriate quadrupole lens formed by, the dynamic voltage can provides an optimal focusing action to the peripheral region of the screen.
However, the use of the in-line self-convergence yoke in the related art electron gun in a CRT results in the R. G. B beams to have fixed spaces at a center of the deflection. According to this, the R beam and the B beam, side beams, become to have a deflection action different from the G beam, a center beam. That is, dynamic voltages provided to the R beam side and the B beam side are boosted for deflecting the R beam and the G beam more than the G beam, to achieve an exact convergence. The boosted dynamic voltages enlarge pixels of the side beams at the peripheral region of the screen, i.e., the side beam pixels become to have halo components. Though it is necessary to drop the dynamic voltages for improving the halo, the drop of the dynamic voltage causes a greater under focusing of the center beam, making the G beam, the center beam, more greater. The unbalance between the center beam and the side beams in the peripheral region deteriorates a resolution in the peripheral region of the screen even if the dynamic quadrupole lens is provided.
Accordingly, the present invention is directed to an electron gun in a color CRT that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an electron gun in a color CRT, which can enhance a resolution in a peripheral region of a screen.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the electron gun in a color CRT having a triode for emitting, controlling, and accelerating R, G, B beams, and main lens forming electrodes for focusing the R, G, B beams emitted from the triode onto a screen, includes first dynamic quadrupole lens forming electrodes for providing a vertical focusing action and a horizontal focusing action to be applied to the R, G, B beams, the vertical focusing action is different from the horizontal focusing action, and second dynamic quadrupole lens forming electrodes for, of the R, G, B beams, providing horizontal/vertical focusing actions to be applied to the R, B beams, side beams, and horizontal/vertical focusing actions to be applied to the G beam, a center beam, the horizontal/vertical focusing actions to be applied to the R, B beams are different from the horizontal/vertical focusing actions to be applied to the G beam, and the first dynamic quadrupole lens forming electrodes and the second dynamic quadrupole lens forming electrodes being arranged in an order starting from the main lens forming electrodes toward the triode.
In other aspect of the present invention, there is provided an electron gun in a color CRT having a triode for emitting, controlling, and accelerating R, G, B beams, and main lens forming electrodes for focusing the R, G, B beams emitted from the triode onto a screen, the electron gun including first dynamic quadrupole lens forming electrodes for providing a vertical focusing action and a horizontal focusing action to be applied to the R, G, B beams, the vertical focusing action is different from the horizontal focusing action, second dynamic quadrupole lens forming electrodes for, of the R, G, B beams, providing horizontal/vertical focusing actions to be applied to the R, B beams, side beams, and horizontal/vertical focusing actions to be applied to the G beam, a center beam, the horizontal/vertical focusing actions to be applied to the R, B beams are different from the horizontal/vertical focusing actions to be applied to the G beam, and third dynamic quadrupole lens forming electrodes for generating a focusing action opposite to the first dynamic quadrupole lens forming electrodes, the first dynamic quadrupole lens forming electrodes, the second dynamic quadrupole lens forming electrodes, and the third dynamic quadrupole lens forming electrodes being arranged in an order starting from the main lens forming electrodes toward the triode.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.